Magneto-inductive flow measuring devices use the principle of electrodynamic induction for the volumetric measurement of flow: Charge carriers of the medium moved perpendicularly to the magnetic field induce an induced voltage in measuring electrodes, which are likewise essentially perpendicular to the flow direction of the medium and, as well, perpendicular to the magnetic field. This voltage induced in the measuring electrodes is proportional to the flow velocity of the medium averaged over the cross section of the tube; it is thus proportional to the volume flow rate.